Microelectronic devices are widely used and are becoming smaller in dimensions, as well as more complex. Manufacturing of such microelectronic devices requires process control using inspection and metrology applied to patterns on substrates (e.g. wafer substrates), as well as identify defects in such patterns. Generally, the structure's properties (geometry and material composition) can be determined by analyzing the optical response of the structure at different wavelengths, different polarization states and/or different directions.
Accurate characterization of the geometrical and material properties of microelectronic devices becomes increasingly challenging, as the critical dimensions become ever smaller and the patterns become more complex. Optical scatterometry (including spectral reflectometry and spectral ellipsometry, etc.) is an extremely effective method for obtaining information on the geometry and material properties of such structures. In this method, broadband light is shone on a sample and collected after being returned from it. By analyzing the returned light of different wavelengths and polarization components of the incident light, incident at different directions, it is possible to obtain information about the structure/sample. Commonly, optical scatterometry is applied to test structures comprised of a repeating array of identical elements, e.g. grating.
Metrology is commonly used to identify specific attributes of the measured structure, such as geometric parameters or material characteristics, and typically utilize spectral measurements. The accuracy by which these parameters can be measured is directly determined by their effect on the measured spectra.
All multiple patterning applications (involving pitch splitting/division) create arrays of lines-and-spaces with overlay appearance as a difference between lines and spaces that are located at the same level (same material and same layer), actually creating multiple critical dimensions (CDs) per period. Such multiple patterning applications include the Litho-Etch-Litho-Etch (LELE) technique, and the Spacer Assisted Double Patterning (SADP) technique. Double Patterning (DP) can create a line CD and two different space CDs for SADP, and up to four different CDs for case of LELE.